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|LETTER TO EDITOR
|Year : 2016 | Volume
| Issue : 6 | Page : 1336-1339
Three sporadic cases of endolymphatic sac tumor
Devimeenal Jegannathan, Gopinathan Kathirvelu, Alamelu Mahalingam
Department of Radiology, Government Kilpauk Medical College, Kilpauk, Chennai, Tamilnadu, India
|Date of Web Publication||11-Nov-2016|
Department of Radiology, Government Kilpauk Medical College, Kilpauk, Chennai, Tamilnadu
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Jegannathan D, Kathirvelu G, Mahalingam A. Three sporadic cases of endolymphatic sac tumor. Neurol India 2016;64:1336-9
Endolymphatic sac tumors (ELSTs) are rare neuroectodermal tumors of the dorsal aspect of petrous part of the temporal bone. They have a low malignant potential, and are locally aggressive tumors of the inner ear having a classical imaging appearance. ELSTs have a high propensity to extend to the middle ear, cerebellopontine angle, and posterior cranial fossa. Tumors vary in size from a few millimeters to several centimeters. We describe three sporadic cases of ELST and review the relevant literature. Awareness of the characteristic imaging findings will help to arrive at a confident diagnosis and help in differentiating ELST from other cerebellopontine angle tumors. Details of the cases are given in [Table 1].
The endolymphatic sac is anatomically located between the posterior periosteum of the mid-portion of the petrous temporal bone and the dura mater of the adjacent cerebellum. The rugose portion of the endolymphatic sac is bony and the distal half lies within the dura. This explains the intra-osseous and posterior fossa components of the mass [Figure 1]e. Tumor growth in the endolymphatic sac will slowly infiltrate and erode the petrous temporal bone. This slow growth is responsible for the long clinical prodrome.
|Figure 1: (a and b) Axial sections of the computed tomography of the brain bone window shows permeative type of destruction (red arrow) of the posterior aspect of the left petrous temporal bone extending to the mastoid. Erosions of the ossicles and inner ear structures are seen with soft tissue in the middle ear. (c) Magnetic resonance imaging sagittal T1 sequence shows mixed intense lesion (arrow) in the cerebellopontine angle region with areas of hyperintensity suggestive of haemorrhage/proteinaceous material. (d) Magnetic resonance imaging T2 FLAIR sequence shows an extra-axial, well-defined lesion (arrow) with multi-cystic appearance and mixed intensity in the left cerebellopontine angle region. (e) Axial T2 sequence. (f) Axial FIESTA sequence confirms the extra-axial location of the multi-cystic lesion causing displacement and compression of the left middle cerebellar peduncle (arrow). (g) Magnetic resonance imaging axial diffusion sequence shows no areas of diffusion restriction. (h) Histopathology slide shows the papillary cystic structures lined with simple cuboidal and columnar epithelium. Siderophages, cholesterol clefts, and clear cells (vacuolated cells) are seen, which are indicative of papillary adenomatous tumor|
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ELST are seen either as a sporadic case or in association with von Hippel–Lindau (VHL) syndrome. Manski et al., reported an ELST incidence of 1:30,000 for the adult population and around 10% for the VHL population. The ELST female-to-male ratio, in a study by Bambakidis et al., was 2:1 in VHL patients and 1:1 in sporadic cases. In our case series, all three patients were male patients and none of them had associated VHL. Bilateral tumors are commonly seen in patients with VHL syndrome (28 versus 1%). Heffner et al., in a study reported the age range to be between 15–71 years. The mean age of presentation has been reported to be 31 years in VHL patients and 52 years in sporadic cases.
The computed tomography (CT) bone window, axial sections reveal the characteristic posterior petrous ridge bony destruction. A small sized tumor typically demonstrates bone erosion centered at the fovea of endolymphatic sac [Figure 2]a and [Figure 2]b or at the external aperture of the vestibular aqueduct., The tumor can demonstrate a thin rim of peripheral calcification that may represent the expanded cortex of the petrous bone  [Figure 3]b and [Figure 3]c.
|Figure 2: (a and b) Axial sections of the computed tomography of the brain, bone window shows the permeative type of destruction (arrow) of the posterior petrous ridge in the region of the endolymphatic sac. The lateral semicircular canal and middle ear ossicles are normal. (c) Magnetic resonance imaging axial T2 sequence shows a heterogenous lesion entering into the fovea of endolymphatic sac (arrow). (d) Magnetic resonance imaging post-contrast T1 sequence shows a heterogenous significant enhancement of the lesion (arrow). Internal auditory canal is well seen and is not involved. (e) Histologic section shows a papillary architecture. The stroma of the papillary fronds are richly vascularized. The papillary structures are lined by a single layer of cuboidal cells|
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|Figure 3: (a) Axial computed tomography of the bone window of the petrous temporal bone shows significant destruction (arrow) of the left posterior petrous ridge extending to the mastoid. (b) Axial magnetic resonance imaging T1 sequence shows a lobulated extra-axial isointense lesion (arrow) with few areas of intralesional signal void and peripheral rim of hypointensity in the region of the endolymphatic sac. (c) Axial magnetic resonance imaging T2 sequence shows the heterointensity of the extra-axial lesion (arrow) and the rim of peripheral hypointensity. (d) Histologic section shows a neoplasm composed of broad papillary configurations lined by a single layer of cuboidal epithelium with fibrovascular stroma|
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On magnetic resonance imaging (MRI), an ELST is commonly seen as a heterogeneous mass with a hyperintense foci in T1 and T2 sequences due to blood products, proteinaceous cysts or cholesterol clefts., The signal voids can be caused by vessels and calcifications. The hypervascular nature of the tumor is demonstrated by contrast enhancement, and inhomogeneity may be due to the enhancement of the solid portion. Flow voids are commonly seen in tumors >2 cm. Calcific density within the lesion can be due to intratumoral calcification or the residual destroyed bone. ELSTs have a high propensity to extend to the middle ear, cerebellopontine angle, and posterior cranial fossa. In a study by Heffner et al., 17 out of 20 cases showed extension to the posterior cranial cavity.
Based on its radiographic extent, Bambakidis et al., proposed a grading system  for ELST, which was hard to correlate with the prognosis. He also proved that VHL patients had a lower grade ELSTs than the sporadic cases.
The glomus tumor is differentiated by the tumor location, An acoustic neuroma, or a schwannoma is differentiated by its location, widening of the internal auditory canal, and no bony destruction. It can have an associated peritumoral arachnoid cyst. Petrous apex granuloma is differentiated by its location, T1 hyperintensity with low signal rim due to hemosiderin and no enhancement of the central area. A cholesteatoma shows diffusion restriction.
Hypervascular metastasis of the renal origin shows nuclear atypia and cells are more commonly tubular than papillary; choroid plexus papilloma is positive for marker transthyretin, and metastatic papillary thyroid carcinoma is positive for thyroglobulin stains.
Two histological types are seen, the mixed type that is generally confined as well as more aggressive, and the locally invasive papillary adenomatous type. ELSTs express many antigens. In immunohistochemistry, they are positive for epithelial membrane antigen (EMA), cytokeratin, vimentin, and periodic acid-Schiff. In addition, they are variably positive for S100 protein, neuron specific enolase, synaptophysin, chromogranin A, and glial fibrillar acid protein.
Complete removal of the tumor is commonly achieved, and at times may necessitate the sacrifice of cranial nerves. When subtotal resection is done, adjuvant radiotherapy is advised. The destructive lesion of the petrous temporal bone with erosion centered at the middle of the posterior margin of the petrous ridge and the site of the endolymphatic sac should suggest the diagnosis of ELST. Familiarity with the classical imaging characteristics helps in early identification of a small or in situ endolymphatic sac tumor, and thereby leading to complete surgical removal and hearing preservation. As VHL patients are at risk of developing bilateral lesions, early diagnosis is critical to avoid bilateral anacusis.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
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